Field calculator won't let me add numbers from an integer field into a text field

Question

I'm trying to field calculate a text field & add digits to it from a 32 bit integer field, by using the expression "ID"+"Fiber Capa" in QGIS 3.28. But the error message

An error occurred while evaluating the calculation string: Cannot convert 'C051-A-' to double

pops up. I'm trying to update the text field so not sure why the message says I'm trying to convert to double.

Answer 1

The error says so, because you are using a + operator. This implies you want to do a mathematical calculation; therefore the attempt to convert the string to double. You could force QGIS to not do that, by converting the number to a string in the first place: "ID"+to_string("Fiber Capa").

But more common, if you want to concatenate, just use || or the function concat() instead: "ID"||"Fiber Capa" or concat("ID","Fiber Capa")